This one is new.
$ fexit <program> args
runs the program until exit or termination, and on that event dumps out a stack
backtrace (and perhaps other information).
Useful for stuff like:
Running testProcMask(frysk.sys.TestSigSet) ...Aborted (core dumped)
where, initially, I'd like to just get a stack-back-trace from that abort() call.